Low temperature thermal radiative properties of gold coated metals

In order to assess the effect of gold deposition on thermal radiative properties of metallic materials, we measured total hemispherical emissivity and absorptivity of Au layers with a minimal thickness of 1 µm in dependence on the temperature TR of thermal radiation (from 20 K up to 320 K). Technically pure copper or titanium alloy (Ti-6Al-4V) was used as substrate while three types of Au layers were deposited by a sputtering process or a galvanic method. Emissivities among samples with Au layers ranged from 1.8% to 3.9% at room temperature. Galvanic deposition of pure Au lowered the original emissivity of Ti-6Al-4V alloy at 300 K from 15.8% to 3.4%, whereas the same deposition on mechanically polished Cu resulted in increase of emissivity by a factor of three, up to 3.2%. Absorptivity of each sample with Cu or Au surface was lower than its emissivity and showed a weaker dependence on TR.